Control method and apparatur



Original Filed Deo.

l, '1927 2 Sheets-Sheet l INVENTOR.

RICHARD P. BROWN www ATTORNEY `Dec. 7, 1937. R, P, BROWN Re. 20,569

CONTROL METHOD AND APPARATUS Original Filed Dec. l, 1927 2 Sheets-Sheet 2 l A INVENTOR.

RICHARD R BROWN yBY A TTORNEY Reiuued Dec. 7, 1937 UNITED STATES phia, Pa.

21 claims.

My invention relates to control methods and apparatus and more particularly, to control methods and apparatus for controlling various physical conditions such, for example, as the regulation of temperature in furnaces, oil still pre-heaters, towers,y gas making machines, chemical retorts, kilns, ovens and the like.

In the practical operation of furnaces and similar devices, mechanisms operated in accordance lo with temperature variations in the furnace from a predetermined temperature as measured by a pyrometer, control the rate of heat supply in accordance with such temperature variations to restore the temperature to the predetermined 15 value.. Inasmuch as there is usually a lag between the rise or fall inl temperature and the change lin fuel supply for restoring the temperatureto the predetermined value, due lto heat capacity and resistance to heat ow of the various l,.vrpnrts, the controller will act to change the rate of heat supply even after the rate of heatsupply is such as to return the furnace to and maintain it at the predetermined temperature, and as a y result the temperature of the furnace will move beyond the predetermined value. 'I'he controller then operates in the reverse direction and the above described operation is repeated carrying the furnace alternately to too high and too low a temperature and causing what is known as hunting. With the usual forms of controllers, hunting furnaces of the tubular oil type still, or in other cases where a furnace in practice is called upon 35 to operate under extreme conditions caused by sudden variations in weather conditions, due to storms, or by sudden variations of the quality or quantity nature of fuel supply or furnace charge.

With the usual controllers, the fuel supply or D heat energy control mechanisms are adjusted to operate between xed limits which are determined by the average condition of the furnace in order to prevent sudden large changes in the rate of fuel supply. If, however, the fuel supply 5 valves are openedvor closed in accordance with or those above mentioned, the sudden change in heat energy supply will ordinarily be far in ex- .:z) cess of the requirement-and will result in' hunting.

The fuel supply valves in order to operate satisfactorily for normal changes are so adjusted that when they are closed to their minimum position the supply of fuel is small enough sol that the temperature does not exceed a predetermined occurs in particularly undesirable manner in large temperature variations accompanying the extreme conditions of an empty or full furnace,y

PATENT GFFICE 20,569 coN'rnoL METHOD AND APPARATUS Richard P. Brown, Philadelphia, Pa., assignor to The Brown Instrument Company, Philadel- Original No.- 1,891,617, dated December 20, 1932, 'Y Serial No. 237.103 December l, 1927. Application for reissue May 4, 1937, Serial No. 140,770

value with an average condition in the furnace.

Y suddenly added to the furnace, or asudden drop in atmospheric temperature occurs, thereby suddenly changing the condition of the furnace, this maximum opening of the valve will not be suilicient to keep the temperature at the predetermined values.

From' extended experiment, I have discovered that a furnace subject to sudden extreme conditions can be controlled automatically to a predetermined temperature in a manner to minimize the unnecessarily large changes in the fuel supply that produce hunting, by operating the fuel supply valves between xedlimits and shifting the limits in accordance with varying conditionsoi' the furnace from an average condition. A primary object of my invention accordingly is to provide methods and means for controlling furnaces operating under extreme conditions to predetermined temperatures substantially without undesirable hunting.

l-Another object of my invention is to provide control means and methods for controlling conditions between limits and varying the limits in accordance with variations of the condition or conditions from a predetermined value or values.

Still another object of my invention is to provide control means automatically brought into operation in the event-ofan abnormal change of condition for bringing the controlled condition back to a normal value with substantially no undesirable hunting.

In order to provide a stabilizing action on the lsystem under control, the controller operates to make a sudden change in the heat supplyor like condition in response to sudden changes of trend of the measured quantity. Accordingly, a further ob'ject of my invention is-to provide means for closing a fuel control valve or other heat energy. control mechanism rapidly and opening it slowly.- In furnaces of comparatively large heat capacity, however, a substantial time lag exists between the change of heat energy supply and theresultant temperature changes. As the controller responds to actual temperature conditions,

fis

it is evident that the usual types of periodic control'apparatus cannot return to the normal or 'predetermined position immediately after the change of heat energy supply, even though a sufficient correction to the supply is made to ultimately bring the temperature to the desired value.Y In applying my invention to this type o1' furnace, a time interval control is provided for Yso adjusting the apparatus that the operation of the limit shiftingv merhanism may be delayed for an interval to prevent operation thereof. if suiiicient correction of the heat supplyenergy has been made to cause restoration to normal without changing the limits 'of' operation of the correcting mechanism.

Accordingly other Aobjects of my invention are to provide means for producing a lag in the variation of heat energy' supply in accordance with changes from a predetermined value, to provide means for renderingv a controller inoperative for intervals of time; to provide means for varying the adjustment of heatA energy supply only* after a predetermined interval Aafter the limits of the measured valuevhave been reached; to .provide means in operating periodic control apparatus whereby several cycles of operation thereof are required before the control apparatus functions: and to provide means whereby a temperature is permitted to respondfffully vto an initial operation of a control apparatusl before the control appa.

ratus again becomesv effective.

Still further objects of my invention will appear in the specification which follows and are defined by the scope of the appended claims. Referring to the drawings:

Figure 1 is a diagram of the control apparatus employed in carrying outr my invention.

Figure 2 is a plan view of a fuel valve controlling mechanism operated between variable limits under control of the control apparatus.A

Figure 3 is a circuit diagram of a modification 1 of my invention.

Referring now more particularly to Figure 1': A contacting control galvanometer is provided comprising a movable coil I Asuspended between the polesof a permanent magnet 2. Secured to vthe coil I is a pointer 3 which-is preferably provided with a downwardly extending portion l adapted to swing in frontfof a graduatedscal 5 to indicate the deviation of the. pointer from normal in the operation ofthe instrument. The pointer 3 is provided with a contact actuating extension 6 which is adapted to coact with carrying springs 1 and 6.' Y

Secured to the springs 1 and 8 arethe electrical contacts 9 and Ill. A block of insulating material II is provided to which are secured the springs 1 and 8 and pointer limiting stops I2.A

Block II supports movable vcontact vtable I3. and secured to the movable contact table I3 are the contacts I4 and I5 whichare adapted to be en gaged by the contacts 9 and III in the operation of the .device as will appear more fully herein'v after. Table I3 is rigidly supported from and movable with a supporting arm I6 which may nasca by a light spring (not shown).

l'Der 29.

' allysupported at 32 with one end thereof prefer- Gear and escapement gears 33 and 39 are separated as shown and are mutilated by removing alternate teeth in each gear so that as springs I8 and I9 will cause the contact table to the distance of one tooth for each reciprocation n of member 31. .This is effected by removing the tated, the gears will be driven to shift the con- 55 embodying a battery B, fixed resistance R and '4278 January 25, 1927, in the tower of a tubular l the motor reversing switches 10 and 10.

22 in any suitable manner and is actuated by` a vertically slidable rod 2'3 suitably guided at 2|. Rod 23 is actuated in its vertical movement'by means of cam 25 against which thelower end of rod 23 is held-due to the weight of the parts or YCam 25 ismounted on a shaft 26 which is driven by the motor 21. 'Mounted onrthe shaft 26 is the cam 28 which actuates a switch mem- An escapement actuating cam 33 also mounted on shaft 26 actuates an arm 3| pivotably held in engagement with the cam 3D by means of a spring 32. The opposite end of arm 3l is pivotally connected at 33- to a vertically extending link 34 which in turn is pivotally connected at 35 to a collar member 36.- Secured to and rotatable in the collar member 36 is anescapement gear member 31 upon which are secured the gears38 and 39 adapted to mesh with the gear 20 and to drive the contact table.

the cam 30 oscillates or shifts gears 38 and 33 alternately into engagement with 'the gear 20 the be stepped backwards by an amount equal to alternate teeth in such a manner from the gears 38 and 39 that the teeth on the gear 39 will be in line with the points where the teeth have been removed from the gear 38.

Member 31 is keyed to and slidably mounted upon the shaft 46 so that as the shaft 4|! is rotact table and as member 31 slides vertically due to the action of the cam 30, the contact table will be permitted to stepbackward to zero position one step for each oscillatory movement of the member 31 along shaft GII.l Shaft l0 is driven by worm gear 4I which in turn is driven by a worm 42l suitably mounted on a shaft 43. Shaft 43 is driven by a worm Wheel or spiral gear v44 which in turn is driven by a worm or spiral gear 45 driven by motor 46.

Galvanometer coil I is connected by means of 'i conductors 53 and 54 through a potentiometer the adjustable resistances R-I and R-2 to the double pole double throw switch 56 which in one position is adapted to vconnect the rpyroxneter or thermocouple 51 in series with the conductors 53 and 5l. Thermocouple. 51 is located at a point where a temperature is to be controlled as for example in the outlet of an oil preheater as shown for example in the patent to Poole 1,615,-

oil still, or in a heating furnace to be controlled.

The motor 21 is connected by means of conductors 53 and 60 and the supply leads 6I and 62. to a source of electrical power. Supply lead 6I of the power source is permanently connected to one lead of motor 46 and the remaining two leads of the motor 46 are adapted to be connected to either one of the remaining power supply leads 62 and 63 by means of the conductors 64 and 66, switch blades 66, 61, 66 and 69 of Blades V66 and 61 are secured to and 'actuated by a member 1I which in turn is actuated by the closing and opening coils 'l2 and. Blades 63 and 63 of the switch 16' are actuated by thev member 1I which in turn is actuated by the closing and sasso l opening coils 1l and 1I. Secured to and operated by members 1| and 14 are the auxiliary circuit closing members 11 and 1l. Circuit closing members 11 and 1l in the open position of the switches 1l and 1I' close break points in the conductor 19. Conductor 1l is connected at one end to power lead l2 of the supply lines. and at its other end is connected to one terminal of each of 'the closing coils 12 and 1l. The other terminals of the closing coils 12 and 1I are connected by means of conductors I and Il to the galvanometer contacts Il and il which in turn are connected to the power supply lead ll by 'conductors Il' and il. The opening coils 1l and 1l have one terminal thereof connected by means of the con-- ductorsor leads 82 to the lead Il and the switch blades Il and Il and have their other terminals connected by means of the conductor through the switch member 2l when closed, and lead 59 to the power lead ll. Connections paralleling those to motor l. are connected to the fuel supply valve control motors Il and |I1 in the man-..

ftlally no-hunting. Thermocoupie 51 is located as pointed out above either in the oil preheater the value it is desired to maintain,l the galvanoml. eter coil is positioned so thatpointer afisin nor-l 4mal or 'zero ;position.'

Motor .21 rotates the' shaft; '2s ccnnnucusyso that the cam actuates-the depressor barx`2| toperiodically. raise and'lower thev .pointer 3.

With the galvanolneter vin zero'position, the

member l willmove'- vertically between'theconthe temperature Areturns tonormal at vsuch a Q- ratethat the galvanometerspointer and =contact tcctspnngs 1 "and s so that neithcrcr the' sets of contacts 9 and il nor-'lil and .iB 'will beclosed.

When the y temperature jat the thermocoupledrifts away from the v-lzrreclct'erxriineil normal tem.. A: perature. condition a deflection inthegaivanom Whentbgmpemtu I :.bqvetheno .ionlpredetermmed value; the galvanorneter point; j i 'shiftto theri'ghtinlfigure I "andsthe ctc;l wm, bc produced with "the-.resine that; the

"pointer s wm be either to theien ci fc the .right-positionland extension '6 will -be P0515. tioned over-the spring1 or l-ln accordancewith Y the direction of the deflection-'of theneetlleorq pointer.' Assuming that the deflection is pro-1,' duced by a drop'in .temperature at .the thermo-v couple and the needle I. inl Figure 1, as the depressorbar 2| 'moves'downf ward, contact l ywill .be-.forcedintoengagement with the contact Il andl an energizing-circuit will be completedfrom conductor 8l' through conductor II', contacts 9 and I4, conductor tl, the

closing coil 15, of the switch 1ii,conductor 19,`

auxiliary switch members 18 'and 1.1 of switches 1l' and 1I to the conductor 62.A

con. 1l cncrgizes, vcloses the switch 10', end..

completes a circuit from the powerv leads 62 and 63 through the switch blades I8 and. to the leads Il and 8l respectively of the motor 4L As switch 10 closes the motor circuit the energizlng circuit for the closing coil is interrupted into rotation and drives the shaft 4l, which throughV the gear; Il will drive the pinion 2l to causethe rotation oi' the contact table I2 in the direction of the deflection of the galvanometer needle.

As the movement of the shaft 26 continues and. afterja predetermined amount of rotation of shaft 4|! has occurred, cam 2l will close the switch -29 and will complete an energizing circuit froinconductor 6I through conductors il and 83, switch 29, coil 18 of the switch 10', conductor l2 to the switch blade Bl and the'power lead l2. .Coil 16 will be energized and will open switch 10' which in turn will cut off the power supply from the motor 46 and cut off the energizing current from the coil 16. Motor 46 will then come to rest, the depressor bar will be on itsV upward movement, and cam 30 will cause the member 31to reciprocate on the shaft 40. As reciprocating movement of the member 31 occurs the spring I 9 will shift the contact table back a distance of one tooth of the gear 2li, the parts being so. proportioned and arranged that normally a plurality of return steps of the contact table under control of the escapement mechanism are required to effect the return thereof to zero or normal position. If the galvanometer deflection is such at the end of the rst correcting cycle that the contact spring 1 is positioned beneath the pointer extension 6, when the bar depresses the pointer 3 in the cycle of operations contacts 9 and il are again closed, the motor 46 will be started into operation to take a further step and the contact table i3 will-be rotated still further to the left of Figure 1. As the fuel supply is increased suiciently the temperature at the couple will rise and the galvanomet-er pointer will startto return to the normal or= zero position. 'I'he motor 21 will continue. to operate the escapement however, causing the table I3 to return to normal. The rate of-return of the contact'table I3 is controlled by thcfescapement mechanism to bersuitamy related to the temperature recovery after. a cor-l rection in the fuel supply .has beenf'madajn table" return to normal at equal ratesnofurther.

*curxje'ctionV willfbe made` until a further-deviation closing coil- 12 'ofl'the'fswitch- 'lliwili be engl-gum vf cuctcrstss. en, cchtacts in ahdifcchductcr se.. 1 v' con 12, cnudctcrjrs; rhechcuitcicsiug-memhers- 1Q and 11Std the power .lead 62.11 This will blades-ea and er cf the switch; 1li'` andn wai ccn-' nect they-laadt! of` motor 'tofthepower supply. Y*

ieaaissandmiiccnnect chc'lca'd 65 tothe pcwel- .Supply Ieadzil vMotor 46" will vrotate" in the reverseV direction end move contacttable ilto the right-' The closure of-the ..switch`:1 0 interrupts the energizing circuit for the'. closing. coil 12 vby vthe movement ofthe'circutclosing member 11'to the-right. Cam 28 will operate to close I the switch 29 as above set forth and an' energizing circuit will be completed through opening coil 13 ofthe switch 10 from the power lead 5|,

conductors 59 and 83, coil 13, conductor 82', to the switch blade 66 and-power lead 63. Opening of the switch 10 will interrupt. the energizing mi l I v Iv..

the parts will come to rest; as the rotation of the shaft 26 continues escapement member 31 will be reciprocated under the influence of the cam 30 and the contact table will return toward normal under the iniluence of spring i8 a step at a time in the manner set forth above. If the pointer and table do not return to normal at the same rate, contacts 9 and I4, or 4l0 and I5 will be operated causing corresponding operations oi' motor 46 which will adjust the fuel supply and will tend to cause the rate of return to normal oi' the temperature to proceed at a rate predetermined by the rate of return of the table.

The operation and proportioning of parts is preferably such thatfor each degree of deviation of the temperature from the normal or predetermined value, one step of the apparatus will be taken. In the form shown the steps are all of equal length but by utilizing well'known -control galvanometers of the form in which the time the contacts are closed depends upon the amount of deilection, the steps may be made proportional in length or interval to the amount of deection of the pointer from the position between contact springs 1 and 8.

Referring now more particularlyuto Figure 2,

rthe fue] varying mechanism operated by the above described controller in accordance with my invention is shown in detail. Motor 84 suitably mounted on the base 84' drives the worm 85 connected to the motor shaft 86'. Y-Worm 85 meshes with worm wheel 86 suitably mounted on shaft 81, through which it drives pinion 88. The gearing 89V comprises a double pinion 89' and 9| which transmits power 'from shaft 81 through pinions 88 and 89 and shaft 90 to the crank disc gear 92.

Secured to the crank disc gear 92 for rotation therewith is the crank disc 94 to which one end of a link 95 is secured at 96. The other end of link 95 reciprocates in guide 91; lA connecting lever 99 is pivoted to the link 95 at |00 by alpin and slot connection which allows oscillation of link 95 by the eccentric. The lever 99 is also connected at to a cross bar |02 and is also pivoted to member 98 at |03. A's the link 95 reciprocates, the connecting lever 99 is rocked about pin |08 as a pivot.

The cross bar |02, has its outer end secured to the valve operating lever |04 at |02. As the connecting lever 99 oscillates about the pivot |03,

this movement is transmitted throughcross bar |02 and rocks the valve operating lever |04 about its pivot |05, through which the fuel valve |06 o! the usual type is operated to its open and closed position. A second cross bar |03' is connected to lever 99 and is adapted to operate an air valve |06 through the lever |04' as clearly shown in Figure 2.

A second motor |01 is properly supported on the base 84' and drives a shaft' |08 which carries a pinion gear |09 at its other end. Pinion gear ||0 meshing with gear |09 is rotatably securedl to shaft and drives the wide face pinion 'I I2. Gear I|3 rotating on the worm ||4 moves between clutches land |I6. Gearing ||1 comprises-,a pinion I|8 secured to the worm ||4 which is driven when the pinion gear ||8 engages either clutch memberI I5 or |I6. Member |20, moving along the worm I9, moves the link |2| secured at one end to member|20 and at its other end at |22 to the member 98. As the member |2| is moved, it rocks the member 98 about its pivot |22. It is evident from the above that the connecting 20,569 l current and the power supply to the motor 46 and Y rod 99` may `either be rocked about pin |03 as a pivot by the reciprocal movement oi link 95 or lmay be rocked about |00 as a pivot by the movement of member 98 operated by link |2I.

The motor |01 is reversible, the direction of rotation depending on the circuits completed as will be described hereinafter. Circuits for motor 84 are completed over conductor |21 to the terminal contacts controlled by the limit switch |28 whichA is of the well known snap acting type. The snap acting switch |28 is pivoted to the base 84 at |29 and secured to the lever 95 at |30. When the motor 84 has operated lto rotate the crank disc 94, 180, the lever 95 moves with a snap action a distance sufiicient to operate the switch |26 to break its upper contact |8| and close its contact |32. motor 84 prepared as shown over contact I3I and conductor |21, themotor will rotate in a direction to close the valve |06 and to simultaneously operate the limit switch |28 to open contact |3I and close |32. This circuit depends however, uponthe closing of the switch blade 61 by the control apparatus as described above. The 'contact |3I is connected by conductor |33' to the high contact side 61 of the control apparatus and the contact |32 is connected by conductor |34' to the low contact side 68 of the control apparatus.

As pointed out in the description of the operation of the invention the motor 84 may be operated either to effect a rotation of the crank disc 94 through 180 in one step or, if preferred, it may be caused to eilect the 180 rotation of crank disc 94 in aI series of steps.

When the motor 84 is operated to rotate disc 94 through 180 in one step, it preferably is used as a non-reversible motor and is operated to effect an opening and closing action of the valves by successive rotation of crank disc 94 through 180 in one direction. The direction of rotation of the motor 84 is the same regardless of whether it is energized through Athe high .or low side of the control instrument. The direction of valve movement eiected by motor 84 is determined by limit switch contacts'l and |32, one or the other of which is in contact making position as determined by the direction of'valve movement last made. The valves are always moved through the limit of movement possible by motor 84 from opened to closed and from closed to opened position in alternate succession. Y

When the motor 84 is replaced by a, motor 84A which is to be operated step by step between the limits of operation of the valve, it is used as a reversible motor and the limit switch |28 is of the ordinary type inl contradistinction to the snap action type. 'I'he motor 84A is then connected in parallel with motor |01.` With motor 84A so arranged, when the limit switch is in intermediate position't-he motor, and the valves, may be operated in either direction in any order and the valvesmay take up a stable position between the extremes of valve movement possible by operation of motor 84A.

In Fig. 2 the motor 84 is shown connected and arranged for non-reversible operation.

In Fig. 3 the circuit connections are diagrammatically shown for operating the motor 84A reversibly.

The motor |01 is connected by conductor |35 to the contact |36 and by conductor |31 to contact '|38 of limit switch |40. The contacts |36 and |88 are controlled by the switch |40 pivotally With the circuit formounted at |4| to the base 34' and pivotally secured to arm |42 which in turn is pivoted to the member 3l. As the member 33 is rocked about pivot |22', thearm |42 is moved to operate the limit switch |40, disengaging contact |38 and engaging contact |38 when the motor |01 has operated its limit, normally, however, this switch maintains its contacts |38 and |38 closed. With the limit switches in the position shown, motor |01 will rotate in a predetermined direction when its circuit is completed by the control apparatus. The motor |01 is a motor connected in parallel with the 3 phase motor 48 so as to be operated to make a valve closing movement when the switch 10 is closed and operated to make a valve opening movement when switch 'I0' is closed.

In order to better illustrate the invention, a detailed description oi' the operation which takes place when the controlled temperature deviates from normal will now be given. It will be assumed that there has been a previous control due to a temperature drop-in the furnace below the desired amount and the switches for both motors are in the position shown in preparation for a' control operation due to a temperature rise above the desired value. If now the temperature being controlled rises above the desired value, the control apparatus operates to close the I/switcl'i 10 which is operated by the making oi the controller high contacts I0 and I.

Circuits are thereupon completed for: both the motors 84 and |01. The circuit for motor 84 extends from the source of power over the blade 01 of switch 10, conductor |33, through the contact |3|. conductor |21 to the winding of the motor 84 and over conductor |38 to the source of power. A circuit is vcompleted for the motor |01 from the source'of power over the switch blade 61 oi switch 10;conductor |33, contact |86, conductor |36'to the motor |01' and over conductor |38 tothe source oi power. It will be noted that the circuit for the motor 04 is completed through the contact |3|, controlled by f the limit switch |28 which is in turn operated -by motor 84 through link 85. The circuit for the motor |01 completed through the contact |36, is opened by the action of the limit switch |40 after the motor |01 has operated to its limit.

As a result of the energizing circuits traced above, both motors rotate. The rotation of the motor 34 operating through the gear mechanism drives thecrank 86 and through it, the link 85 moving connecting lever 88 about its pivot |03. The lever 88 drives crossbars |02 and |03', which in turn operate to close the valves |06 and |06A respectively through the valve operating levers |04 and |04. The control instrument operates to maintain switches 10 and 10' closed through non-operative for further closing of the valve o should the control continue vto close its high contact side 61.

During this period while motor 84 is operating although the motor |01 is rotating driving the pinion |.I3 through the gear mechanism including pinions |08 and H0, this is not effective at this time to control the valve due to the back lash or lost motion while pinion ||3 is moving along the worm I4 towards the clutch I I6 and is therefore atthis time not transmitting any energy for operating vthe valves. If however, after the valves have been operated to the maximum position attainable by the motor 34 the temperature is not restored to the predetermined value and the controller' therefore continues to close contact 31 the kfurther rotation oi motor |01 rotates the pinion I I3 until it engages the clutch I I6. Thereafter it will transmit the power from the motor |01 through to the link |2| for rotating the member 88 about its pivot |22'.

The connecting member 88 is thereupon operated through pin |03 by which it is secured to member 88 and moves about |00 as a pivot to in turn move the cross bar |02 to the right as in the case of its movement under control of motor 84 described above. The valve operating lever |04 is now operated a-iurther step. In this manner the valve will continue closing in steps until there is a suiiicient reduction in the fuel supply to restore the temperature to the predetermined condition. As a result oi' the step by step operation of the valve by the motor |01 new valve limits are obtained so that the voperation of the motor 84 will now normally operate the valve mechanism between the limits which are different than those Afor which the valve was originally adjusted. For

each periodic operationof the controller closing the contact 61 motor |01 will operate the valve inthe manner described above until the temperature drops to the predetermined value. At the limit of its movement, however, the limit switch |40 will move to disengage its contact |36.

Il the temperature drops below the value at which it is to be maintained, the controller Figure 1 operates to engage its low contacts V8 and I4 thereby closing switch 10'. A circuit will be completed for the motor 84 from the source oi power over -the switch blade 68 of switch 10', conductor |34', contact 32, now closed by the limit switch |28, conductor |21, motor 84 and over conductor |38 to the source of power. This circuit completed overconductor |21 rotates the motor 84 which in turn drives the valve mechanism |06 from a substantially closed to open position between the new limits determined by the previous operation thereon by motor |01.

If the valve having been operated to its maximum open position still does not suiilciently increase the fuel supply to restore the temperature to its normal value, the control apparatus will continue to close the switch 10 repeatedly. During this period a circuit is completed for motor |01 from the source of power over blade 68 of switch 10', conductors |34 and |34, contact |38, conductor |31 to motor |01, over conductor |38 to the source of power. The motor rotates in the reverse direction from that described above. While the control apparatus periodically closes the contact on its low side, the motor |01 drives the gear. ||3 over the worm ||4 in the reverse direction from that described above to take up the back lash due to the movement of the gear ||3 from the clutch ||6 to the clutch H6. I1' after this period, the temperature still does not attain the desired value, motor |01 will operate the valve |06 through clutch ||6 and lever |2|, member 88 and levers 88, |02 and From the above description, the operations will now be apparent. While a single motor may be arranged to add or subtract a certain amount ot for every change in temperature, it cannot change the normal amount to take care of abnormal changes in the temperature of the furnace. For this reason, the second motor is brought into operation, if after an interval of time, the operations of the first motor have failed to restore l the condition to its normal value, and adds or subtracts from the definite amount of operation of the first motor. Y

When the motor 84 is arranged for a complete lopening or closing action of valve |04 in a single step, the motor 04 operates to effect an on and oif control between narrow limits. The limits of operation of the valves by motor 84 are made as narrow as circumstances will permit to take care of ordinary fluctuations of the temperature or other measured condition under control. Accordingly, the motor 84 alone operates to maintain the measured temperature within a narrow range, within which the temperature hunts, the fluctuation of the temperature within the narrow range causing operation of motor 84 which increases and decreases the fuel supply to cause the temperature to swing back and forth within the narrow temperature range. If the motor 84 alone were used to effect the control, it would be necessary to widen the limits of operation of the valves by it so as to provide a change of heat supply which would be effective to counteract any change in conditions, such as fuel quality and pressure, atmospheric temperature and humidity, load on furnace, et cetera, however great such change might be. Under such conditions the temperature range which it would be possible to maintain by automatic control would be far too large. By the use of motor |01, which acts to change the range or limits through which the valves may be operated by motor 84, it is possible to make that range narrow and correspondingly to make narrow the range within which the temperature may be maintained by automatic control.

After the'fuel valve has been operated to its limit by the motor 84 and the temperature does not change accordingly during a reasonable period of time which depends in each case upon local conditions and may adjustably be varied by the amount-of back lash, determined by the positions of clutches ||5 and ||6, it is obvious that further adjustmentof the valve is required. This is accomplished through the operationv of motor |01 which transmits power through one of the clutches |I5 and ||6 for operating the valve beyond the limits to which it is operated by motor 84.

vIt should be 'apparent from the description above, that when a change in temperature occurs vthe motor 84 performs the first or initial operation on the valve. After the motor 84 has operated the valve to its limit and the temperature condition still continues off normal the motor |81 becomes operative to further move the fuel valves after a reasonable interval of time adjustably determined by the back lash provided in the pomtion of the clutch members. 'nie mode of operation of the control system asa whole, that is, the control instrument. of 1 and the two motor mechanism of Fig. 2

combined and electrically associated inthe man- ,ner hereinbefore described, will now be described.

'Let it be assumed by way of illustration, thatthe control system is applied to a furnace, that the instrument measures by a thermocouple the temperature of the material being treated. oil for exfuel to or from a predetermined normal amount ample, the temperature of which is to be maintained constant, that the valve |06, (and valve |06' for steam or air also if desired), be in the fuel oil line so that adjustment of the valve will adjust the fuel supply and accordingly the heat supply to the furnace.

When the furnace, specincally a tube still, is brought into operation the exit oil temperature, to be maintained constant, is abnormally low. Accordingly, the defiecting member of the meter tends to take up a position down-scale considerably below the control point of the instrument. The down-scale tendency of the pointer 3 brings it over low contacts 8. and I4, overshooting being prevented by a stop l2 on the movable contact table. The continuously operating motor 21,

`through cam 25 and depressor 2|, moves pointer 3 periodically to make low contacts 8 and |4. Making of contacts 8 and |4 closes switch 10' which remains closedwhen pointer 3 is released until cam 20 and switch 28 opens it. While closed, switch 10' `operates motor 46 to move the contact table in the direction of pointer deflection, downscale; also, switch 10' operates motor 84 ln one step through the full range of valve movement which is possible by operation of motor 84, provided such an adjustment had not been made previously; also, switch 10' operates motor |01 a step proportionate to the time switch 10 is closed. Since the measured temperature is abnormally low the initial movement of the contact table does not move contacts 8 and |4 clear of pointer 3, accordingly switch 10' is again closed followed bythe consequent operation of motors 46 and |01, motor 84 not being operated again so long as the pointer 3 is moving in the same direction, downscale, because of the actuation of limit switch |28 upon the initial valve opening operation of motor 84. So long as the pointer 3 moves downscale the above described operations are repeated. The motor` |01 eventually moves gear ||3 into engagement with the proper clutch ||4 or IIE, if not previously so engaged, so that further operation of motor |01, through members |2I, 88, 88, |02 and |04 e'ects a further opening of valve |06 to increase the fuel' supply.

The abnormally low temperature incident 4to starting the furnace will cause the controller to operate motor |01 to its limit as determined by limit switch |40 thereby admitting a maximum supply of fuel. During the above described operation of the control instrument the escapement 20, 38, 39 allows repeated small steps of the contact table back toward neutral. However, under the conditions specified, the adjustv ment `o1 the contact table by motor 46 is the predominating effect and causes the table to follow the pointer to its limit of movement. After the table has been moved to the position where the pointer 3 is at rest the escapement will allow such table movement as to bring the low contacts 8 and |4 into engageable position relative to the pointer thereby operating motor 01 to its limit, if the motor has not been so operated, and

:sov

furnace and' oil but greatly in excess o! the heat` supply sufilcient to maintain the desired exit oil temperature once it has been established. Such :an excess of heat supply tends to cause overshooting of the exit oil temperature. To prevent such overshooting, either altogether or partially,

' it is necessary to reduce the heat supply in anl ticipation oi' the arrival of desired exit oil temperature. n the contrary it is desirable to bring the exit oil temperature and general furnace operatingv conditions to normal as quickly as possible. In order to meet both of these Qonflicting desiderata it is necessary to maintain a maximum heat supply as long as possible and then to reduce the heat supply quickly. Other conditions of desirable operation incident to maintaining the tube still in normal operation, which will be considered hereinafter, must be met.

As the measured temperature starts to rise the pointer begins to move upscale and, due to the action of the escapement, the contact table like- Vwise moves up-scale. However, the rate of heat supply is such as to cause the pointer 3 to move up-scale more rapidly than the escapement permits the contact table to move so that the pointer 3 is moved into position relative to the table for actuating high contacts I0 and l5. Actuation of high contacts |0 and I5 takes place similarly to the actuation of contacts 9 and I4 and results in closing switch 10. When closed, switch operates motor 84 to its limit in one step in a direction to partially close valve |00 thereby reducing the fuel supply substantially;

switch 10 also operates motor 40 to move the contact table to follow the pointer; and switch 10 operates motor |01 in the reverse direction to its previous' operation thereby moving gear ||3 away from the clutch which it previously engaged. The initial large valve adjustment by motor 04 allows the controller to be u sed so as to maintain maximum fuel supply for maximum time and then to reduce the fuel supply quickly. The movement of the contact table by motor 46 brings its neutral in register with the pointer thereby tending to prevent further operation of contacts I0 and I5. The reduction in valve opening due to operation of motor 84 reduces the rate of temperature rise considerably, however, the

extent of valve adjustment for which motor 84 is designed is determined largely by factors, later to be considered, and is not sufliclent to check the temperature rise, therefore the heat supply usually will still be sulciently great to cause overshooting of the exit oil temperature. The escapeent mechanism is designed to cause the control table to move toward the control point ofthe instrument at a rate which is determined largely by those characteristics of steady furnace operation which determine the rate at which the exit oil temperature may vary from normal. Therefore,the rate of movement of the control table is slow and the pointer 3 will advance into position for actuating high contacts I0 and I5 as it moves toward the desired temperature position. Such actuation 'causes further operation ofA motor |01 with corresponding movement of gear ||6 from one clutch toward the other clutch and operation of motor 46 to adjust the contact table so as to bring its neutral into alignment with the pointer. Such operation continues as the pointer moves upscale, the gear ||6 eventually engaging theclutch and operating to further reduce the valve opening thereby reducing the heat supply and the rate of temperature rise. Since 'nasca the heat supply at the start was greatly in excess of that required for steady operation of the furnace and since the characteristics of the furnace during steady operation largely determine the design of the control mechanism, the operation of the controller in reducing the supply of fuel during the rise in the temperatureof the exit oil ordinarilyis not sumcient to prevent overshooting oi' the exit oil temperature, however, the extent of overshooting is greatly reduced by the above described operation of the automatic control mechanism.

As the temperature rises 4above the desired exit oil temperature the pointer I continues to make contacts I0 and Il and to operate motor |01 to close valve |06 further; also motor 46 is operated to move the table up-scale to follow the pointer, As the controller continues to so operate the-heat supply is diminished more and more and the rate of increase of exit oil temperature decreases until temperature stops rising and begins to fall. The extent to which the exit oil temperature overshoots the desired temperature and to which the valve position overshoots the optimum position is small compared to extent of overshooting incident to starting the furnace in operation because of the anticipating action of the control mechanism. Therefore, the rate of temperature fall is slow and approximates that rate of temperature fluctuation which .obtains during steady operation of the furnace to make a large opening increment in the valve |06, simultaneously motors |01 and 46 are operated as before described, the motor |01 acting to move gear ||3 away from the valve closing clutch. The action of motor 04 greatly reduces the rate of'temperature fall and will approximately stabilize the temperature of the exit oil at an even level. This action .will take place when the exit oil temperature is approximately that desired and the furnace proceeds in steady operation.

During steady operation of the vfurnace thev exit oil temperature approximates the optimum and the heat supply approximates that which is necessary to replace the heat losses continually taking place so that the heat flow or transfer is `inapproximately steady stateand the ratev of exit oil temperature fluctuation is small. Inasmuch as the temperature to be held constant is the measured temperature actuating the controller it is obviously necessary that the measured temperature must fluctuate about the optimum temperature slightly to actuate the controller. It is desirable to maintain 4that range of fluctuation as small as possible, accordingly when the temperature xises above orfalls below the optimum temperature it is desirable to change the heat supply as quickly as possible and in a direction and to an extent such as to cause the temperature trendto reverse as quickly as possible. Such operation is made possible by the use of motor 84. When the temperature is rising the limit switch |20 will be in positionrto permit a closing increment o'f valve by operation of motor 04. When the pointer reaches a position to actuate the high contact the motor 04 will be operated in one step to effect such a closing action in valve |00 as to reduce the heat supply immediately and sufllciently to stop further temperature rise and cause the temperature to fall which will continue until the pointer makes the low contacts when the reverse operation takes place causing a reverse of temperature trend. The motor |01 is actuated simultaneously with the operation of motor 00 butv due to the lost motion between gear ||0 and its clutches it usually does not operate the valve. Sufticient lost motion is provided to allow time for the change in heat supply by motor 04 to affect the exit oil temperature. Thus motor 0I is operated by the controller to cause the exit oil temperature to oscillate between narrow limits about the optimum temperature. When furnace operating conditions change so much that the range of valve movement by motor 0I will n ot compensate for the changed heat transfer conditions the motor |01 is operated to adjust the valve thereby, in eect, changing the limits of valve operation for motor 04. Such changes which necessitate the operation of motor |01 ordinarily occur gradually so that the motor' |01 operates slowly. Such l operation of motor |01 takes place as follows:

As the changing furnace conditions tend/to cause the exit oil temperature to fall for example, the low contacts are made more frequently than the high contacts, the'motqr 0I operating to maintain the exit oil temperature between the desired limits. Such unbalanced operation of the high and low contact operates motor |01 to take up the lost motion between gear I I 3 and the valve opening clutch so that eventually motor |01 will operate valve |00 to increase the heat supply sufliciently to compensate for the deficiency, in heat transferred which tends to cause the exit oil temperature to fall. This controlaction can and usually will take place without allowing the exit oil temperature to depart from the predetermined range about the optimum temperature.

f Sudden large changes in furnace operating con ditions are taken care of in the manner described in connection with the starting of the furnace.

From the above'descrlption of the mode of operation of this invention it is seen that the control instrument, because of the contact table follows the pointer, operates in .accord with ternperaturetrend and therefore provides a stabilizing control action, the more rapid the rate of temperature change the more counteracting control action is exerted thereby preventing the system under control from getting out of hand; that, due to the escapement, the control instrument .is biased to a predetermined operating temperatureto which it proceeds while continuously exv ercising a strong stabilizing control action on the furnace; that the controller operates, by virtue of motor 0l to maintain the measured Vtemperature within exceedingly narrow limits; and that, by virtue of motor |01 it compensates for cumulative temperature trends. Thus a controller is provided which functions in a plurality of ways, each of its functions being best adapted to produce a desired control effect, the combination and interaction of such control functions in one controller making it possible to so design the' controller that the desired control effects largely ,A determine such allotment of control action to the various control functions conducive to the highest degree of closenessJ of control and the maximum of flexibility for satisfying the many and valve change operation of which it is capable.

When the motor 0IA is used as a reversible motor inparallel with motor |01 operating rapidly but in a plurality of steps between its limits of operation, the mode of operation of the invention as above outlined is substantially the same. Whether the motor be used to operate in a single step or in a plurality of steps, its chief function is to provide a stabilizing action which takes place quickly and produces a suiljlcient change in the heat supply to cause a reversal of temperature trend when the tendency of the temperature to depart from normal is that normally encountered in steady operation of a furnace. In some cases it may be of advantage to use the motor 00 operating between its limits of plurality of steps in order that the motor 01 may take up a position intermediate of its limits which will more nearly correspond to the optimum temperature which it is desired to maintain, thus the temperature may be caused to line out upon the optimum temperature desired whereas by contrast. when the motor 80 is operating throughout its range in a single step the temperature will be` caused to fluctuate within narrow limits about the optimum temperature and never be allowed to settledown or line out upon the optimum temperature.

I-n the above description, the invention isdescribed as applied to the shifting of valves in a fuel line. It is obvious, however, the the invention is also applicable to other methods of controlling fuel supply as for example changing the ratios of a transformer or shifting a contact cn a resistance. It will be noted also that a controller with an escapement return is illustrated although any other form of controller such for exampleas those operating on the principle of graded control in accordance with the extent of departure of the temperature from northat the control can be'accomplished from a diierent furnace position foreach motor. For example/the most important temperature in tube still oil cracking processes is the temperature attained in the tower. Variations in tower temperature occur due to changes in the oil outlet chamber and to independent causes such for example as weather changes. Such variations of temperature in the tower occur so late that they have heretofore not been eifectively available to ycontrol the heater, and it has therefore been found most expedient to control the temperature from outlet loil temperature of tubular stills, the nearest position to the tower at which temperature variations occur in time control the heater in reasonably satisfactory manner. Such controls cannot, however, correct for tower temperature extraneous conditions such as weather conditions. I- have discovered that it is practical to control the fuel supply from the tower temperature with the mechanism heretofore described by controlling the motor 84 in accordance with the outlet temperature of the oil to maintain the oil outlet temperature substantially constant, and controlling .motor |01 from the .soV

tower temperature so that if the tower temperature varies with a given oil outlet temperature, the oil limits of the mechanism will be changed to change the oil outlet temperature being maintained to maintain a predetermined tower temperature. In this way it will be seen that a novel and effective tower temperature'control correcting for oil temperature as well as extraneous conditions is provided.

My improved controls maybe further modified by operating motor Il from the temperature of the combustion chamber instead of the oil outlet temperature and motor |01 from the tower temperature, providing another eifective means of maintaining oil at a predetermined temperature in a practically satisfactory manner.

Although I have illustrated my invention in connection with temperature c ontrol in a tubular oil still and with a particular type of graded or follow-up contacting galvanometer controller having an escapement return mechanism, it will be apparent to tloseskilled in the art that my invention has broader applications in the control art and that any Well known graded or on and oil types of contacting galvanometer or other control mechanism may be utilized, and I do not intend to limit myself by the specific application herein shown, but only insofar as set ,forth in the appended claims.

I claim:

1. In a control system, a device to be maintained at a predetermined temperature, a motor mechanism for controlling the rate of fuel supply to said device and a control mechanism for variably operating said motor mechanism in accordance with the variations in temperature of said device from a predetermined temperature, said control mechanism comprising a galvanometer with a pointer movable from a normal position in accordance with the departure of said temperature from said predetermined value and contacts controlled lby said Vpointer when deflected from its normal position, the contacts being arranged to move in the direction of the deflection of said pointer, said motor mechanism being arranged under predetermined conditions to be non-operative to vary said fuel supply in response to the ilrst few operations thereof by said control mechanism.

2. In a control mechanism, a device to be maintained at a predetermined temperature, a motor mechanism for controlling the rate of fuel supply to said device and a control mechanism for varimotor being non-operative to control the fuel supply under predetermined conditions for the `first few operations thereof by said control mechanism and a second motor for varying the fuel supply, said second motor being operativev during said period while said first mentioned motor is non-operative.

3. In a control system, a device to be malntained at a predetermined temperature, a' fuel control device, means for varying said fuel control device between predetermined limits, a second n means for controlling the fuel control device for trol mechanism comprising a galvanometer withy a pointer movable from. a normal position in accordance with the extent' of variation of said temperature from said predetermined temperature, contacts controlled by said pointer when deflected from its normal position and arranged to move in the direction of said pointer, said control mechanism being arranged to operate said firstmentioned means when said pointer is deflected to vary the rate of fuel supply to said device between said limits and arranged after said first mentioned means has operated said fuel supply to its limit to operate the second mentioned means to extend said limit, in the event the temperature continues to remain off normal.

4. In combination, a device to be maintained at a predetermined temperature, a control mechanism, temperature responsive means for variably operating said control mechanism, a ilrst motor controlling the rate of fuel supply to said device, a second motor for controlling the rate of fuel supply to said device, periodically operating means cooperating with said control mechanism for selectively operating said first and second motors at different rates and to different limits respectively and means controlled by said control mechanism and periodic means for varying the operation of said control `mechanism whereby said motors are operated in accordance with the rate of change of the temperature of said device.

5. In combination, a device to be maintained at a predetermined temperature, a control mechanism, temperature responsive means for operating said control mechanism so long as the temperature differs from the predetermined normal temperature, an initial motor for controlling the rate of fuel supply to said device, a floating motor for controlling the rate of fuel supply to said device, periodically operating vmeans cooperating with said control mechanism for selectively operating said initial and said floating motors at different rates and to diierent limits respectively and means controlled by said control mechanism and periodic means for varying the operation of said control mechanism whereby said control mechanism responds to the rate of change of the temperature of said device. l

6. An automatic system for producing or maintaining a predetermined condition comprising means responsive to departure from said predetermined condition, first and second motor means selectively and variably operated by said first named means for decreasing, by increments which varyl with the magnitude of said departure, the rate of change of a quantity in response to which said'departure from said predetermined condition is reduced and said predetermined condition attained and timing "mechanism for determining the time in which said rst and second motor means cooperate to establish a predetermined condition. l y

7. An automatic system for producing or maintaining a predetermined condition, comprising a mechanism responsive to the departure from said predetermined condition tending to render itself inoperative before said predetermined condition is said means establishes the predetermined condition.

8. The combination, with a device to be heated, of means for delivering heat theretmautomatic mechanism responsive to the departure of said device from a predetermined temperature, comprising a temperature responsive device, a deflecting member controlled thereby, an initial motor mechanism operable between predetermined limits by said deecting member, a floating motor selectively and variably controlled by said deflecting member when deflected for varying the haat input to said device, means controlled by said deflecting member tending to cause said automatic mechanism to become non-operative for any temperature to which the temperature ,respznsive device is subjected, and means for preventing said mechanism from becoming nonoperative until said device attainssaid predetermined temperature whereby the heat input into said device is varied until said predetermined temperature is attained.

9. In combination with a device to be heated of means -for delivering heat thereto, an initial motor mechanism, floating mechanism forv controlling the rate of delivery of said heat delivering means, said initial motor mechanism being operable to control the rate of heat delivery between predetermined limits and said floating mechanism being arranged to change said limits, automatic means responsive to the departure of said temperature from a predetermined temperature comprising a device responsive to the temperature of said furnace, an electric circuit controlled thereby, a galvanometer in said circuit having a de fleeting member for controlling said initial and' floating motor mechanism and means controlled by said deflecting member when deflected to cause the variation in said heat delivery to said device byV means of decreasing increments which carry with the magnitude of said departure.

10. 'Ihe method of predetermining temperature A which comprises varying the supply of heat in large quantities with avariation of temperature from a predetermined temperature and thereafter varying the heat supply at regular intervals in small increments of predetermined magnitude as long as the temperature is away from the predetermined temperature.

1i. In combination, a devic'e to be maintained at .a predetermined temperature, a fuel supply therefor, a first motor for controlling the'rate of fuel supply to said device, a second motor for controlling the rate of fuel supply to said device, a control mechanism comprising a galvanometer and a deilecting member, means responsive to the variations in temperature of said device from said predetermined value for deflecting said member, means controlled by said member when deflected for selectively operating said motors to effect different rates of Vfuel supply respectively, means controlled by said motors to varythe fuel supply for restoring said temperature to the predeter mined value and means operated by said deflecting member tending to render said control mechanism non-operative to control said motors.

12. In combination, a device to be maintained at a predetermined temperature, a fuel supplyA therefor, a first motor for controlling the rate of fuel supply to said device, a second motor for controllingthe rate of fuel supply to said device, a control mechanism comprising a galvanometer and deilecting member, means responsive to the variations in temperature of said device from said predetermined value i'orv defiecting said'member,

deflected position.

eratlve.

. for controlling the supply of heat to said oil heater, control means operated in accordance.

the measured temperature from a predetermined means cooperating with said member when deflected for operating said motors at different predetermined rates and t'o different predetermined operative after aninterval of' time and means whereby said cooperating means is operative following said operations of said motors tending to render said member non-operativeV to control said motors.

13. In combination, a device to be maintained at a predetermined temperature, a fuelsupply therefor, a first motor for controlling the rate of fuel supply to said device, a second motor for` i controlling the rate of fuel supply to said device, a control mechanism comprising a galvanometer and a deflectng member, means responsive to` the variations in temperature of said device from said predetermined value for defiecting said member, periodic means cooperating with said member when deected for operating said motors at different predetermined rates and to dierent predetermined limits respectively, means controlled by said motors for varying the fuel supply to restore said temperature to the predetermined value, and means controlled by said periodic means and member tending to render said control mechanism non-operative to control said motors. 14. In combination, a device to` be maintained at a predetermined temperature, a fuel supply therefor, a first motor for controlling the rate of fuel supply to said device, a second motor for controlling the rate of fuel supply to said device, a control mechanism comprising a galvanometer anda deecting member, means responsive to the variations in temperature of said device from said predetermined value for deflecting said member, means controlled by said member when deflected for operating saidl motors at differentl predetermined rates and to dierent predetermined limits respectively, means controlled by said motors for varying the fuel supply to restore said temperature to the predetermined value and means whereby under predetermined conditions said member is rendered non-operative to control said motors while in a l5. In combination, a deviceto be maintained at a predetermined temperature, a fuel supply therefor, a first motor for controlling the rate of fuel supply to said device, a sec- 1 ond motor for controlling the ratev of fuel sup-` ply to said device, a control mechanism comprisinga galvanometer and a Vdeectlng member, means responsive to the variations in temperature of` said device from said predetermined value for defiecting said member,A means controlled by said member when deflected for operating said motors at different predetermined rates and to different predetermined limits respectively,-means controlled by said motors for varying the fuel supply to restore said temperature to the predetermined value, and follow up means controlled by said defieoting member tending to render said control mechanism non-op- 16. In combination, a tubular oil heater, temperature responsive means measuring the temperature of the oil, first and second motor means with the rate and the extent of the variations in normal for operating said first motor to vary the supply oi heat to said heater between xed limits and for operating said second motor, said second motor being normally non-operative during the rst few operations of said control means and arranged vto become operative after an interval of time to further vary said supply of heat to said oil heater.

17. An apparatus for maintaining a predetermined temperature comprising a rst fuel controlling means operating to vary the fuel supply in accordance With the rate of change, of the temperature to or from a predetermined temperature, and a second fuel controlling means operating to further vary the fuel supply after a predetermined fuel change has been effected n by the said first fuel controlling means.

18. A controller having a measuring device responsive to the condition to be controlled, control instrumentalities associated with said measuring device and operating according to the rate of change of the measured quantity so long as the measured quantity is off normal, and means for adjusting the condition to be controlled operated by said instrumentalities, said means acting to make a large adjustment incident to a sudden change in trend of the measured quantity and to make additional adjustments at a slow rate when the measured quantity is departing from normal.

19. A controller for heat exchangers comprising a measuring instrument responsive to the ltemperature of the material under heat treatment. a. control instrument operable by said measuring instrument, said control instrument operating according to the rate of temperature change, according to the extent of temperature departure from normal, and according to the direction of temperature departure from normal, heat supply adjusting means operable by said control instrument for making large initial adjustments in the heat supply to the heat exchanger in response to sudden temperature changes and for making additional adjustment in the heat supply at a slow rate in response to continued temperature deviations.

20. A controller having a measuring device responsive to the condition to be controlled and including an element deilecting in accordance with the value of the measured quantity, control instrumentalities associated-with said measuring device and operating according to the rate of change of the measured quantity so long as the measured quantity is off normal, and including' a member coacting withsaid element to produce a control action dependent on the relative positions of said element and member and means for giving said member a movement minimizing the displacement from said member of said element as the latter deects away from its normal position and tending after each such movement to move said member at a denite rate back toward its normal position, and means for adjusting the condition to be controlled operated by said instrumentalities and including a device acting to make a large adjustment incident to a sudden change in trend in the measured quantity and including a device adapted to make additional adjustments at a slow rate when the measured quantity is departing from normal and also when itis approaching normal at a rate dierent from the rate at which said member is returning to its normal position.

21. A controller for heat exchangers comprising a measuring instrument responsive to the temperature of the material under heat treatment, a control instrument, operable by said measuring instrument, said control instrument operating'according to the rate of temperature change, according to the extent of temperature departure from normal, and according to the direction oi temperature departure'from normal, heat supply adjusting means operable by said control instrument and including one motor for making large initial adjustments in the heat supply to the heat exchanger in response to sudden temperature changes and another motor for making additional adjustment in the heat supply at a slow rate in response to continued temperature deviations.

RICHARD P. BROWN. 

